@jknott Yep. I had tried, but that didn't work. No connection. No ping, no nothing. Reported elsewhere. ARP or what, no clue yet. Had to (1) re-allocate interfaces (in this case, swapping). Trouble is also physical access, after a reboot. Crawling into some dungeons. The box has neither monitor nor keyboard.
No, it must be pre-set.
(Don't want to whine about 'good old days', and yet, my former Soekris/m0n0wall was just running along. Power off - power on and I had access through the web interface for everything else. Have tried hard, but not found anything on the same level of ease and reliability. Well, updates and performance made it a no-go.)